The present invention is directed to a data communications system and is useful with systems employing groups of pulses directed to various receivers. The pulses in a particular group can represent different information to the same receiver. In more detail the present invention includes such a system in which one or more of the transmitted pulses functions as a "key", and this key is utilized by the specific receiver to determine the significance--in the qualitative sense, identifying the nature of the data represented--of other data pulses in the same group, or of pulses in other groups.
Different systems for transmitting data in a series of pulses groups are known and used. Examples of such systems are depicted and explained in U.S. Pat. No. 4,394,655, entitled "Bidirectional, Interactive Fire Detection System" which issued July 19, 1983; U.S. Pat. No. 4,470,047, with the same title, which issued Sept. 4, 1984, and U.S. Pat. No. 4,507,652, with the same title, which issued Mar. 26, 1985. The teachings of these patents are incorporated herein by reference. In these patents a controller (transmitter) communicates with one or more transponders (receivers) over a two-wire system. Communication could also be over any other form of data bus. In those patents the communication is by data bursts or groups of pulses, as represented generally in FIGS. 5 and 6 of the '655 patent, and in FIGS. 4 and 5 of the other two references. In these systems the high-amplitude portions of a data pulse group were used to transmit commands from the controller, and the low-amplitude portions were used to return information from the addressed transponder to the controller. Such an arrangement has proved very effective in systems employed in the life safety and property protection fields. In these earlier patents four different bits of information could be returned in a single data pulse group. Increasing complexity of data communication systems and more widespread use of such arrangements has identified a need for returning more data than is possible with the described system, without significantly affecting the cost or complexity of the enhanced operating system, or the time required to send and/or receive all the desired data.
It is therefore a primary consideration of the present invention to provide an improved data communication system in which data is transmitted as different bits in a group of data bits, or pulse group, but in which the number of different data types which can be transmitted in a single pulse group substantially exceeds the number of data bits in a single group.